It is known to add a magnetic device on top of the reference plane of a level to allow the level device to be fixed to the top of a metal surface. As for magnetic devices used in levels in the contemporary market, usually several holes are punched on the reference plane of the level, the magnet and a magnetically conductive iron piece are fixed on top of a plastic piece, and then the assembly is installed inside the already punched and well-machined hole. This structure easily causes the straightness of the reference plane to be broken and influences the precision of the level, and at the same time, the externally exposed iron piece easily rusts and influences the external appearance of the level. Moreover, when the magnetic seat is installed in the wrong position, the precision of the level can be negatively affected.